Code that Writes Code

I have scripts that re-create my databases for testing and development purposes. But sometimes I want to take the data from a set of tables and move it as well – I could use SSIS, or a SELECT INTO statement, but what if I want to “re-set” the data to a point in time? In other words, load it with some “base data”?

I thought this might be a good place to demonstrate “code that writes code”. No, it isn’t that big of a deal – most DBAs know how to do this, but in the interest of those who don’t, I thought I would share.

So the end result I want in this case is to have a bunch of INSERT statements that contain my base data from a table where that data already exists. I could script out the table from SSMS and use the replacement parameter feature to fill out each record individually:

I have a table in one of my databases that I right-clicked to show the INSERT statement:

-- Person

INSERT

INTO [WAVS].[dbo].[Person]

([PersonName]

,[Street]

,[CityStateZip]

,[PersonType])

VALUES

(<PersonName,varchar(150),>

,<PersonStreet,varchar(100),>

,<PersonCityStateZip,varchar(255),>

,<PersonPersonType,varchar(100),>)

I can use the CTRL-SHIFT-M keys to replace the VALUES part with the values I want.

But I already had a copy of that “base” data before I turned the database over to the testers. Before I give it to them, I run code like this on each table – this one is for the Person table above (note that there should only be two lines here):

All I have to do is copy those statements into my “initialization” scripts just after the table creations, and then I can run them at will to create my new database (I know I can take a backup – I have reasons for not doing that).

There are two keys for writing code that writes code: The first is to simply use the single tick (') to write out what the end code should say (INSERT INTO, in my case) and then to use multiple ticks (''') when you want the code to contain the ticks themselves. This “escapes” the characters so that you can embed them. If you use SSMS to write your queries, the color coding will look as mine does above. You’ll also need to remember to CAST or CONVERT any data types that don’t concatenate (+) together well. In my case I had to CAST an integer value – but that’s OK, since it is only printing to the screen and I don’t include the ticks, the INSERT works fine.

You can use this method not only with INSERTS, but with lots of operations. And you can also even fire off the code once you create it – but that’s another post :)